It is widely disclosed that 2-phenoxypyrimidine, or (pyrimidin-2-yl) oxybenzene derivatives are useful as herbicides, for instance, in Arg. Biol. Chem., Vol. 30, No. 9, p. 896 (1966), and Japanese Unexamined Patent Publication No. 55729/1979 and so on. Among 2-phenoxypyrimidine compounds developed in recent years, particularly, some 2-(pyrimidin-2-yl)oxybenzoic acid derivatives have invited great attention in the art because of their potent herbicidal activities.
In the prior art, as 2-(pyrimidin-2-yl)oxybenzoic acid derivatives, there have been known a large number of compounds, as disclosed in European Patent Publication No. 223,406, No. 249,708, No. 287,072, No. 287,079, No. 315,889, No. 321,846, No. 330,990, No. 335,409, No. 346,789, No. 363,040, No. 435,170, No. 435,186, No. 457,505; GB Patent Publication No. 2,237,570; DE Patent Publication No. 3,942,476 and so on.
These compounds in above mentioned publications show herbicidal mode of action similar to that of sulfonyl ureas, imidazolinones and triazolopyrimidines well-known as typical amino acid biosynthesis inhibitory herbicides, and also have merits of being easily prepared with their simple structures.
From the investigation on the herbicidal mode of action, it was revealed that the above known compounds impair the activity of ALS, i.e., Acetolactate Synthase; and which is known to involve in the procedure of synthesizing Acetolactate at the first stage of the biosynthesis pathway of essential amino acid, valine, isoleucine, etc., from pyruvic acid in plant body.
In this connection, it was reported on the study of enzyme activity assay using ALS by Peter B. et al., that 2-(pyrimidin-2-yl)oxybenzoic acid esters are pro-herbicides which have no herbicidal activities in themselves, and are only active after hydrolysis with carboxylesterase in plant body to their free acid forms [Peter B. et al., Pestic. Sci., Vol. 30, No. 3, p 305-324 (1991)].